Heat butter and brown sugar in a skillet. Add half of the milk and stir until sugar dissolves and mixture comes to a boil. Cook covered 2 to 3 minutes. Uncover and cook until mixture resembles taffy. Combine egg yolks, flour, butter and remaining milk. Stir until smooth. Add to hot mixture, stirring constantly, until thick. Pour into pastry shells and top with meringue. Brown in 350° oven for 2 to 3 minutes or until brown.